Method to selectively etch silicon nitride to silicon oxide using surface alkylation

Abstract

Embodiments of processes and methods that provide selective etching of silicon nitride are disclosed herein. More specifically, new processes, methods and etch chemistries are provided to selectively etch silicon nitride layers formed on a substrate, while protecting silicon oxide layers formed on the same substrate. In the method embodiments, a substrate having a silicon nitride (SiN) layer and a silicon oxide layer formed on the same substrate is exposed to an alkylating agent, which reacts with the amine groups on the exposed SiN surfaces to form an alkylated surface layer on the SiN layer. The substrate is exposed to a fluorinating agent to remove the alkylated surface layer and selectively etch the SiN layer without significantly etching the silicon oxide layer. The disclosed methods can be used to selectively etch silicon nitride over silicon oxide using a wet or dry process.

What is claimed is: 
     
         1 . A method of selectively etching silicon nitride over silicon oxide using a chemical vapor etching (CVE) process, the method comprising: 
 receiving a substrate having a silicon nitride layer and a silicon oxide layer exposed on a surface of the substrate;   exposing the surface of the substrate to a vapor-phase alkylating agent, which reacts with an exposed surface of the silicon nitride layer to alkylate amine groups on the exposed surface of the silicon nitride layer and form an alkylated surface layer on the silicon nitride layer; and   exposing the surface of the substrate to a vapor-phase fluorinating agent to remove the alkylated surface layer and selectively etch the silicon nitride layer without etching the silicon oxide layer;   wherein said exposing the surface of the substrate to the vapor-phase alkylating agent reduces or prevents formation of a gas-phase reaction byproduct, which is capable of catalyzing etching of the silicon oxide layer, during said exposing the surface of the substrate to the vapor-phase fluorinating agent.   
     
     
         2 . The method of  claim 1 , wherein an etch selectivity of the silicon nitride layer to the silicon oxide layer is greater than 15:1. 
     
     
         3 . The method of  claim 1 , wherein said exposing the surface of the substrate to the vapor-phase alkylating agent and said exposing the surface of the substrate to the vapor-phase fluorinating agent are performed sequentially with no overlap in time. 
     
     
         4 . The method of  claim 3 , wherein the surface of the substrate is exposed to the vapor-phase alkylating agent to form alkylamine groups on the exposed surface of the silicon nitride layer, and wherein when the substrate is subsequently exposed to the vapor-phase fluorinating agent, fluorine atoms within the vapor-phase fluorinating agent react with the alkylamine groups to produce reaction byproducts, which are vaporized from the exposed surface of the silicon nitride layer to selectively remove the alkylated surface layer from the silicon nitride layer. 
     
     
         5 . The method of  claim 3 , wherein the surface of the substrate is exposed to the vapor-phase fluorinating agent for an amount of time sufficient to remove the alkylated surface layer without: (a) etching the silicon nitride layer underlying the alkylated surface layer, or (b) forming the gas-phase reaction byproduct capable of catalyzing etching of the silicon oxide layer.  
     
     
         6 . The method of  claim 3 , further comprising repeating said exposing the surface of the substrate to the vapor-phase alkylating agent and said exposing the surface of the substrate to the vapor-phase fluorinating agent to selectively etch a predetermined amount of the silicon nitride layer.  
     
     
         7 . The method of  claim 3 , wherein said exposing the surface of the substrate to the vapor-phase alkylating agent comprises exposing the surface of the substrate to a first process gas containing an alkyl halide. 
     
     
         8 . The method of  claim 7 , wherein the alkyl halide is a bromide, chloride or other halide of a hydrocarbon.  
     
     
         9 . The method of  claim 7 , wherein the alkyl halide is ethyl bromide (CH 3 CH 2 Br) or methyl bromide (CH₃Br).  
     
     
         10 . The method of  claim 7 , wherein said exposing the surface of the substrate to the vapor-phase fluorinating agent comprises exposing the surface of the substrate to a second process gas containing fluorine atoms. 
     
     
         11 . The method of  claim 10 , wherein the second process gas comprises hydrofluoric acid (HF), difluoride (F 2 ), xenon difluoride (XeF 2 ) or nitrogen trifluoride (NF 3 ).  
     
     
         12 . The method of  claim 10 , wherein the first process gas is an anhydrous ethyl bromide (EtBr) vapor and the second process gas is an anhydrous hydrofluoric acid (HF) vapor. 
     
     
         13 . The method of  claim 1 , wherein said exposing the surface of the substrate to the vapor-phase alkylating agent and said exposing the surface of the substrate to the vapor-phase fluorinating agent are performed concurrently with at least some overlap in time. 
     
     
         14 . The method of  claim 13 , wherein the vapor-phase alkylating agent reacts with the amine groups on the exposed surface of the silicon nitride layer to form alkylamine groups, and wherein the vapor-phase fluorinating agent reacts with the alkylamine groups to produce reaction byproducts, which are vaporized from the exposed surface of the silicon nitride layer to selectively remove the alkylated surface layer from the silicon nitride layer. 
     
     
         15 . The method of  claim 13 , wherein the vapor-phase fluorinating agent reacts with the exposed surface of the silicon nitride layer to form the gas-phase reaction byproduct capable of catalyzing etching of the silicon oxide layer, and wherein the vapor-phase alkylating agent reacts with the gas-phase reaction byproduct to form an alkyl amine gas and reduce a concentration of the gas-phase reaction byproduct to prevent etching of the silicon oxide layer.  
     
     
         16 . The method of  claim 13 , wherein said exposing the surface of the substrate to the vapor-phase alkylating agent and said exposing the surface of the substrate to the vapor-phase fluorinating agent comprise exposing the surface of the substrate to a gas mixture comprising a first process gas containing the vapor-phase alkylating agent and a second process gas containing the vapor-phase fluorinating agent.  
     
     
         17 . The method of  claim 16 , wherein the first process gas contains an alkyl halide. 
     
     
         18 . The method of  claim 17 , wherein the alkyl halide is a bromide, chloride or other halide of a hydrocarbon.  
     
     
         19 . The method of  claim 17 , wherein the alkyl halide is ethyl bromide (CH 3 CH 2 Br) or methyl bromide (CH₃Br).  
     
     
         20 . The method of  claim 17 , wherein the second process gas comprises hydrofluoric acid (HF), difluoride (F 2 ), xenon difluoride (XeF 2 ) or nitrogen trifluoride (NF 3 ).  
     
     
         21 . The method of  claim 17 , wherein the first process gas is an anhydrous ethyl bromide (EtBr) vapor and the second process gas is an anhydrous hydrofluoric acid (HF) vapor.